Location: The Crab State! In other words, Maryland.
Yes, It depends on the tank size. And, just to clarify, and pet peeve of mine is when people say their betta is lonely. Bettas don't "get lonely" or "want friends" because in the wild they're solitary fish.
Daily 'companionship' for Lakitu is just watching me watch him. He likes to be pointed at, instead of mirrors.
To add what people said about the betta getting "lonely", bettas actually can get pretty stressed out with tank mates. A lot of people pick shrimp who are bottom dwellers. Bettas like mid and top tank.
That said, make sure you know what you're getting into with tank mates, tank needs to big enough and feeding requirements need to be in check. ADF's are pretty dumb in finding food and betta's often starve them by stealing their food ^.^